A technique for the measurement of estrogen receptors in prostate using a protein analysis column of an HPLC system has been developed at our Institution. This has been facilitated by the availability of 16 alpha 125 Iodo-Estradiol. This newly developed technique has been validated by using a traditional system for the measurement of estrogen receptors (immature rat uterus). Prostatic specimens from 13 patients have been evaluated thus far and the only elevations on estrogen receptors have been found in patients with prostatic carcinoma. The importance of the development of such techniques is the fact that now we can measure estrogen receptors in small needle biopsy samples in prostate tissue making possible the wide clinical use of such a procedure.